Detecting Gross Fetal Movements Using Fetal Magnetocardiography

Abstract

Fetal development is associated with the emergence of fetal movements (FM). Gross FM involve the limbs and/or the trunk and are accompanied by changes in heart rate and heart rate variability (HRV). To detect such FM, we developed a semi-automatic technique which analyzes changes in signal morphology of multichannel fetal magnetocardiogram (FMCG) signals over time. The technique exploits the changes QRS signal shape and amplitude in specific channels resulting from gross FM. From our database of FMCG records, we selected 26 five-minute FMCGs in 14 healthy pregnant women (31st-41st week of gestation) in which FM were suspected on the basis of fetal heart rate accelerations. In each recording, after the removal of the maternal artifact, the fetal QRS complexes were identified using template matching. In each channel, the minimum and maximum amplitudes of each QRS complex were determined. In the actogram, the beat-to-beat changes in maximum and minimum values, respectively, were quantified using the variance over a 20 beat window. Automatically determined, rapid increases in variance were considered reflecting changes in fetal position. The timings of these increases were examined together with changes in fetal heart rate (determined by the RR intervals derived from the QRS complexes). We found between 1-4 episodes of rapid increases in variance in each of the 26 actograms. These episodes were associated with an immediate decrease of 31.7±18.8 ms from overall RR interval (heart rate increase: 11.3±6.5 bpm). Beat-to-beat RR interval variability was reduced from overall 7.4±3.2 ms to 3.8±1.7 ms immediately following the begin of the actographically determined episodes. The results suggest that the majority of the episodes reflected FM and that this actographic approach may be used to automatically scan FMCG recordings for such movement. This will be helpful in categorizing FMCG recordings with respect to fetal behavioral state and improve the assessment of fetal HRV.